Race and sex associations with tacrolimus pharmacokinetics in stable kidney transplant recipients

Using maximum plasma concentration (Cmax) to personalize taxane treatment and reduce toxicity

Taxanes are a widely used class of anticancer agents that play a vital role in the treatment of a variety of cancers. However, toxicity remains a major concern of using taxane drugs as some toxicities are highly prevalent, they can not only adversely affect patient prognosis but also compromise the overall treatment plan. Among all kinds of factors that associated with taxane toxicity, taxane exposure has been extensively studied, with different pharmacokinetic (PK) parameters being used as toxicity predictors. Compared to other widely used predictors such as the area under the drug plasma concentration curve versus time (AUC) and time above threshold plasma drug concentration, maximum plasma concentration (Cmax) is easier to collect and shows promise for use in clinical practice. In this article, we review the previous research on using Cmax to predict taxane treatment outcomes. While Cmax and toxicity have been extensively studied, research on the relationship between Cmax and efficacy is lacking. Most of the articles find a positive relationship between Cmax and toxicity but several articles have contradictory findings. Future clinical trials are needed to validate the relationship between Cmax and treatment outcome and determine whether Cmax can serve as a useful surrogate endpoint of taxane treatment efficacy.

DQB1 antigen matching improves rejection-free survival in pediatric heart transplant recipients

BACKGROUND

Presence of donor-specific antibodies (DSAs), particularly to class II antigens, remains a major challenge in pediatric heart transplantation. Donor-recipient human leukocyte antigen (HLA) matching is a potential strategy to mitigate poor outcomes associated with DSAs. We evaluated the hypothesis that antigen mismatching at the DQB1 locus is associated with worse rejection-free survival.

METHODS

Data were collected from Scientific Registry of Transplant Recipients for all pediatric heart transplant recipients 2010-2021. Only transplants with complete HLA typing at the DQB1 locus for recipient and donor were included. Primary outcome was rejection-free graft survival through 5 years.

RESULTS

Of 5,115 children, 4,135 had complete DQB1 typing and were included. Of those, 503 (12%) had 0 DQB1 donor-recipient mismatches, 2,203 (53%) had 1, and 1,429 (35%) had 2. Rejection-free survival through 5 years trended higher for children with 0 DQB1 mismatches (68%), compared to those with 1 (62%) or 2 (63%) mismatches (pairwise p = 0.08 for both). In multivariable analysis, 0 DQB1 mismatches remained significantly associated with improved rejection-free graft survival compared to 2 mismatches, while 1 DQB1 mismatch was not. Subgroup analysis showed the strongest effect in non-Hispanic Black children and those undergoing retransplant.

CONCLUSIONS

Matching at the DQB1 locus is associated with improved rejection-free survival after pediatric heart transplant, particularly in Black children, and those undergoing retransplant. Assessing high-resolution donor typing at the time of allocation may further corroborate and refine this association. DQB1 matching may improve long-term outcomes in children stabilized either with optimal pharmacotherapy or supported with durable devices able to await ideal donors.

Gender and kidney transplantation

Kidney transplantation provides the best form of kidney replacement therapy with improvement in quality of life and longevity. However, disparity exists in its availability, utilisation and outcomes, not only due to donor availability or financial constraints but also arising from the influence of biological sex and its sociocultural attribute i.e., Gender. Women make up the majority of kidney donors but are less likely to be counselled regarding transpantation, be waitlisted or receive living/deceased donor kidney. Biological differences also contribute to differences in kidney transplantation among the sexes. Women are more likely to be sensitised owing to pregnancy, especially in multiparous individuals, complicating donor compatibility. A heightened immune system in women, evidenced by more autoimmune illnesses, increases the risk of allograft rejection and loss. Differences in the pharmacokinetics of transplant drugs owing to biological variances could also contribute to variability in outcomes. Transgender medicine is also increasingly becoming a relevant topic of study, providing greater challenges in the form of hormonal manipulations and anatomic changes. It is thus important to determine and study transplantation and its nuances in this backdrop to be able to provide relevant sex and gender-specific interventions and design better practices for optimum kidney transplant utilisation and outcomes.

The association between tacrolimus exposure and tremor, headache and insomnia in adult kidney transplant recipients: A systematic review

PURPOSE

Tremor, headache and insomnia have been linked to the immunosuppressant, tacrolimus. The aim of this systematic review was to determine if there is a correlation between tacrolimus exposure and new-onset tremor, headache and insomnia experienced by adult kidney transplant recipients.

METHODS

PubMed, Embase, Cochrane Library and CINAHL databases were searched up to 11 April 2023 for published studies which reported on tacrolimus exposure in adult kidney transplant recipients, alongside information on treatment-emergent neurologic manifestations, including tremor, headache and insomnia. Review articles, case studies, conference abstracts and articles not published in English in peer-reviewed journals were excluded. The Physiotherapy Evidence Database and Newcastle-Ottawa Quality Assessment Scales were used to assess risk of bias. Extracted data was analysed via a narrative synthesis.

RESULTS

Eighteen studies involving 4030 patients in total were included in the final analysis. These comprised five randomised control trials and thirteen observational studies. Studies failed to find significant association between tacrolimus trough concentrations in whole blood and the incidence of neurologic side effects such as tremor, headache and insomnia; however, in one study the incidence of toxicity requiring a dose reduction increased with increasing, supratherapeutic targeted levels. Females, especially Black females, and older age were positively associated with the prevalence of neurologic adverse effects. Results were conflicting regarding whether extended-release formulations were associated with fewer neurologic complications than immediate-release formulations.

CONCLUSION

The varied study designs and criteria for reporting tremor, headache and insomnia impacted on the quality of the data for exploring the relationship between tacrolimus exposure and the onset of neurologic manifestations experienced after kidney transplantation. Studies that examine defined neurologic complications as the primary outcome, and that consider novel markers of tacrolimus exposure while assessing the potential contribution of multiple covariate factors, are required.

A Physiologically Based Pharmacokinetic Approach to Recommend an Individual Dose of Tacrolimus in Adult Heart Transplant Recipients

Tacrolimus is the principal immunosuppressive drug which is administered after heart transplantation. Managing tacrolimus therapy is challenging due to a narrow therapeutic index and wide pharmacokinetic (PK) variability. We aimed to establish a physiologically based pharmacokinetic (PBPK) model of tacrolimus in adult heart transplant recipients to optimize dose regimens in clinical practice. A 15-compartment full-PBPK model (Simbiology® Simulator, version 5.8.2) was developed using clinical observations from 115 heart transplant recipients. This study detected 20 genotypes associated with tacrolimus metabolism. CYP3A5*3 (rs776746), CYP3A4*18B (rs2242480), and IL-10 G-1082A (rs1800896) were identified as significant genetic covariates in tacrolimus pharmacokinetics. The PBPK model was evaluated using goodness-of-fit (GOF) and external evaluation. The predicted peak blood concentration (Cmax) and area under the drug concentration-time curve (AUC) were all within a two-fold value of the observations (fold error of 0.68-1.22 for Cmax and 0.72-1.16 for AUC). The patients with the CYP3A5*3/*3 genotype had a 1.60-fold increase in predicted AUC compared to the patients with the CYP3A5*1 allele, and the ratio of the AUC with voriconazole to alone was 5.80 when using the PBPK model. Based on the simulation results, the tacrolimus dosing regimen after heart transplantation was optimized. This is the first PBPK model used to predict the PK of tacrolimus in adult heart transplant recipients, and it can serve as a starting point for research on immunosuppressive drug therapy in heart transplant patients.

Bayesian optimization of tacrolimus exposure in stable kidney transplant patients

STUDY OBJECTIVE

The objective was to compare tacrolimus AUC0-12 determined by Non-Compartmental Analysis (NCA) using intensive sampling to Maximum a Posteriori-Bayesian (MAP-Bayesian) estimates from robust (n = 9 samples/subject) and sparse (n = 2 samples/subject) sampling in 67 stable KTRs and a validation group of similar patients.

DESIGN

This open-label, prospective, single center 12-h PK study included nine serial samples collected in KTRs to determine steady-state NCA tacrolimus AUC0-12 .

SETTING

This study was conducted at a single site within a large, urban hospital in the western New York area.

PATIENTS

This study described tacrolimus pharmacokinetics in stable kidney transplant recipients on maintenance tacrolimus therapy.

INTERVENTION

Robust and sparse AUC0-12 estimates by a MAP-Bayesian approach were obtained using the Advanced Dosing Solutions (AdDS) and ADAPT5 freeware. Limited sampling strategies were evaluated using the original population PK model (n = 67), which was also assessed using a validation group (n = 15). AUC0-12 agreement was tested by paired t-tests with intraclass correlation coefficient (ICC) and Bland Altman analysis.

MEASUREMENTS AND MAIN RESULTS

A total of 35 Black and 32 White stable KTRs (estimated glomerular filtration rate [eGFR] = 55.2 ± 15.7 mL/min/1.73m2 ) received the tacrolimus dose of 3.4 ± 1.7 mg/study with troughs of 6.8 ± 1.8 ng/mL. The NCA-AUC0-12 was 123.8 ± 33.6 μg·h/L compared to MAP-Bayesian estimates for Robust-AUC0-12 of 124.7 ± 33.3 μg·h/L and optimal 2-specimen Sparse-AUC0-12 of 119.7 ± 32.7 μg·h/L for the training group. Comparison of Robust-AUC0-12 to NCA-AUC0-12 had an ICC of 0.96 (p = 0.99) while comparison of Robust-AUC0-12 to Sparse-AUC0-12 using Pre-dose trough [C(t0h )] and 1 h [C(t1h )] resulted in an ICC of 0.93 (p = 0.014). In the validation group, 5 Black and 10 White KTRs (eGFR = 56.4 ± 16.8 mL/min/1.73m2 ) received a mean tacrolimus dose of 1.9 ± 1.2 mg/study with a trough of 6.0 ± 1.7 ng/mL. The validation group's NCA-AUC0-12 (88.4 ± 33.1 μg·h/L) was comparable to Robust-AUC0-12 (85.1 ± 33.8 μg·h/L, ICC = 0.93; p = 0.12) and Sparse-AUC0-12 determined from C(t0h ) and C(t4h ) (86.7 ± 33.9 μg·h/L, ICC = 0.91; p = 0.61).

CONCLUSION

MAP-Bayesian estimation for patient-specific AUC0-12 using sparse, two-specimen sampling is comparable to NCA and may enhance tacrolimus TDM in stable KTRs.

Comparison of P-glycoprotein function in peripheral blood mononuclear cells ex vivo in stable Black and White male and female kidney transplant recipients

Kidney allograft survival remains poorer in Black compared to White recipients due to racial differences in calcineurin inhibitor (CNI) pharmacology. P-glycoprotein (P-gp), an ABC efflux transporter expressed in peripheral blood mononuclear cells (PBMCs), modulates CNI pharmacokinetics and intracellular pharmacology. This study investigated P-gp function in PBMC ex vivo at 0 (trough), 4, 8, and 12 h in stable Black and White male and female kidney transplant recipients (n = 67) receiving tacrolimus and mycophenolic acid. Tacrolimus doses were adjusted to troughs of 4-10 ng/ml. P-gp function was quantified with flow cytometric measurement of cyclosporine (CYA; 2.5 μM)-reversible efflux of P-gp substrate, 3,3'-Diethyloxacarbocyanine iodide by determining the percentage change of mean fluorescent intensity (MFI) with CYA (% ΔMFI). The composite parameter of area under the concentration versus time (AUC)0-12h % ΔMFI estimated P-gp function. Data analysis examined race, sex, and race-sex associations to P-gp function. A secondary aim analyzed ABCB1 genotypes: 1236C>T (rs1128503), 2677G>T/A (rs2032582), 3435C>T (rs1045642), and P-gp function. P-gp function (% ΔMFI) was higher in White patients at troughs (p = 0.031) compared to Black counterparts with similar trends at 4 and 8 h. Reduced AUC0-12h % ΔMFI was noted in Black recipients (N = 32) compared with Whites (N = 35, p = 0.029) with notable pairwise adjusted differences between Black and White women (p = 0.021). Higher AUC0-12h % ΔMFI was associated with ABCB1 2677 TT compared to GG variants (p = 0.035). The AUC0-12h % ΔMFI was greater in White than Black subjects. P-gp function was higher at troughs in White subjects and differed between race-sex groups. P-gp function in PBMC may influence intracellular tacrolimus exposure and inter-relating pharmacodynamic responses which may support race and sex pharmacologic differences.

Representation of Women in Contemporary Kidney Transplant Trials

Women are often underrepresented in clinical trials. It is unclear if this applies to trials in kidney transplant (KT) and whether the intervention or trial focus influences this. In this study, the weighted participation-to-prevalence ratio (PPR) for women enrollees in KT trials was determined for leading medical transplant or kidney journals between 2018 and 2023 using meta-regression overall and in three sensitivity analyses by: 1) Whether the intervention involved immunosuppression; 2) Area of trial focus; rejection, cardiometabolic, infection, lifestyle, surgical; 3) Whether the intervention was medical/surgical or social/behavioral. Overall, 33.7% of participants in 24 trials were women. The overall pooled PPR for the included trials was 0.80, 95% CI 0.76-0.85, with significant heterogeneity between trials (I ² 56.6%, p-value < 0.001). Women had a lower PPR when the trial involved immunosuppression (PPR 0.77, 95% CI 0.72-0.82) than when it did not (PPR 0.86, 95% CI 0.80-0.94) and were less likely to participate in trials with a medical/surgical versus behavioral intervention; the lowest PPR for women was in studies examining rejection risk (PPR 0.75, 95% CI 0.70-0.81). There is better representation of women in KT trials compared to other medical disciplines, however women remain underrepresented in transplant trials examining immunosuppression and rejection.